1. Field of the Invention
The invention concerns filters or traps that remove particulates from the exhaust of diesel engines and is particularly concerned with traps containing perforated hollow tubes, each of which is wound with heat-resistant yarn to provide the filtering element.
2. Description of the Related Art
Coassigned U.S. patent application Ser. No. 07/681,147, filed Apr. 5, 1991 (Bloom) discloses a diesel particulate trap having a casing containing at least one perforated hollow tube which is helically cross-wound with a heat-resistant yarn (e.g., resistant to temperatures above about 600.degree. C.) that has a core from which filaments or fiber segments projects outwardly. The core of each convolution of the yarn is radially aligned with the core of an underlying convolution to form walls that are spaced to define four sided openings. The projecting fiber segments intermesh across each opening. Means for blocking spaces at the ends of the casing require exhaust entering an unblocked space at one end of the casing to pass generally radially through the four sided openings, thus allowing the intermeshed filaments or fiber segments to trap soot or particulate carried by the exhaust. Diesel particulate traps illustrated in the Bloom application have several tubes that either are concentric or in a side-by-side arrangement.
Because of the high temperatures at which accumulated soot is periodically burned off, the yarn should be ceramic, and preferably continuous-filament, ply-twisted ceramic yarn to afford sufficient strength to allow the yarn to be wound tightly to stay in place against the force of the exhaust. A continuous-filament, ply-twisted yarn can be texturized to cause loops of continuous filaments to project outwardly without substantial breakage of filaments. Especially useful are continuous-filament ceramic yarns of alumina-boria-silica fibers available commercially as NEXTEL.TM. 312 or 440 ceramic yarn from the 3M Co. A diesel particulate trap as per the Bloom application made with texturized ceramic yarn should be at least as efficient and durable as any known diesel particulate trap, but because of the high cost of the ceramic yarn, it may be thought to be too expensive for general use.
The disclosure of the Bloom application is incorporated herein by reference.